Polyurethane foams, formed by the reaction of a polyisocyanate with a polyhydroxyl-containing compound in the presence of a suitable catalyst, are widely accepted as padding materials for cushions in furniture, automobiles and the like. Polyurethane foams are also used in sponges, personal care and hygiene items and as specialty packaging materials.
The use of a polyol in the preparation of polyurethanes by reaction of the polyol with a polyisocyanate in the presence of a catalyst and perhaps other ingredients is well known. Conventional polyols for flexible polyurethane foams, such as slab urethane foams, are usually made by the reaction of a polyhydric alcohol with an alkylene oxide, usually ethylene oxide and/or propylene oxide, to a number average molecular weight of about 2,000 to 5,000 and above. Polyols have been modified in many ways in attempts to improve the properties of the resulting polyurethane, for example, by using a polymer polyol as the polyol component. Conventional polyols may be used as the dispersing media or base polyol in these polymer polyols.
For example, dispersions of polymers of vinyl compounds such as styrene, acrylonitrile or a mixture of the two (abbreviated as SAN monomers), or of polyurea polymers, such as those prepared from toluene diisocyanate (TDI) and hydrazine in conventional polyols have been included to improve the properties of the polyols, and thus, the properties of the resulting foam. Polyurethane foams with higher load bearing properties (ILD--indentation load deflection, and CFD--compression force deflection) may be produced in this manner. It would be desirable if polymer polyols could be prepared which would be stable and have low viscosities. Stability is important to the storage life of the polyols before they are used to make the polyurethane foams. The tendency of polymer polyols to undergo phase separation if they are not stabilized is well known. Dispersants are often used to help keep the polymers in the dispersion. Low viscosities and small particle sizes are also important in a good quality polyol to permit it to be pumped easily in high volume foam producing equipment.
It would further be desirable if styrene/acrylonitrile polymer polyols could be synthesized which would have large SAN ratios. The substitution of styrene for acrylonitrile in these polymer polyols helps prevent discoloration during the cure of the polyurethane, and also helps improve flame retardability of the resultant foams. However, the stability of the polymer polyols decreases with increasing styrene to acrylonitrile ratios. Viscosity and particle size are also typically adversely affected with high styrene contents.
The present invention involves the reaction products of homo- or copolymers containing anhydride groups with polyols. Patents are known which relate to the polymerization of monomers having anhydride groups. For example, U.S. Pat. No. 3,085,986 teaches low pressure molding compositions containing a mixture of a polyhydric alcohol having at least one primary hydroxyl group and a solid, linear low molecular weight copolymer of maleic anhydride and styrene which is cross-linked by the alcohol. U.S. Pat. No. 4,198,488 describes the addition of an anhydride monomer to a polymer polyol composition. The product itself is the final polymer polyol: a dispersion of solid particles, and not a preformed soluble dispersant. Stable, fluid polymer polyols made by the free radical polymerization of a monomer mixture of an .alpha.,.beta.-ethylenically unsaturated dicarboxylic acid anhydride and a copolymerizable monomer in an organic polyol medium of secondary hydroxyl terminated polyol are disclosed in U.S. Pat. No. 4,721,733 to Gastinger and Hayes.
Also of interest is the English abstract to Japanese Application 1004228 relating to dispersants for non-aqueous systems comprising a copolymer of alkyl vinyl ether or alpha olefin, and maleic acid anhydride and a polyether polyol or its derivative having a number average molecular weight of 400 to 50,000. See also the English abstract to Japanese Application 1004227 which discusses dispersants in nonaqueous systems obtained by reacting polyether polyols with copolymers of alkyl vinyl ethers or alpha olefins and maleic anhydride. Both of these latter abstracts note that the dispersant is used for dispersing inorganic or organic pigment particulates in nonaqueous media, e.g. oily paint, oily ink, magnetic tape, etc.
To prepare polymer polyol dispersions with high styrene contents and high solids contents, it is the practice in the art to employ polyols which contain specified and ostensibly critical amounts of induced unsaturation, as shown in U.S. Pat. Nos. 3,823,201; 4,454,255 and 4,690,956, among others. These polyols with induced unsaturation are typically prepared by reacting polyols with an unsaturated monomer such as maleic anhydride or the like. U.S. Pat. No. 4,539,340 also relates to the reaction of polyols with monomeric anhydrides.
Stable, low viscosity polymer polyol compositions comprising a continuous phase, a disperse phase within the continuous phase, and a dispersant for enhancing the stability of the resultant polymer polyol are disclosed according to U.S. Pat. No. 5,021,506. In one embodiment, the dispersant is formed by polymerizing at least one acrylate monomer in a polyether polyol to form a single phase homogeneous liquid intermediate reaction product which is transesterified to form a polyol polyacrylate dispersant.
It is well known in the an that high styrene, high solids content polymer polyols are desirable, but difficult to prepare in stable form. There remains a need for novel dispersants for use in preparing polymer polyols that have relatively high styrene contents, but which also have good stability, small particle sizes, and low viscosity as well.